A linear light polarizing filter allows light having an electric field in a certain plane to transmit at a higher rate than light having an orthogonal electric filed. Polarizing filters have been widely used in, for example, ophthalmic products, display devices, imaging devices and optical communication devices. Polarizing ophthalmic lenses are interesting because they have the unique ability to preferentially eliminate glare that is reflected from smooth horizontal surfaces such as water and ice.
Dichroic materials have been used for the manufacture of light polarizing articles. Dichroic materials, when properly oriented, can preferentially transmit light polarized in a particular direction. Such dichroic material may be polarizing over a relatively wide spectrum, such as the visible spectrum, or they may have the polarization property over a narrow range of wavelengths. A group of dichroic material is called pleochroic dyes. A pleochroic dye molecule has varying absorption depending on the orientation of the electric field of the incident light. Some pleochroic dyes are self-orienting when placed on a suitable substrate, whereas others have to be combined with other materials to produce the polarizing effect.
As taught by U.S. Pat. No. 2,400,877, an oriented dichroic dye layer may be formed by depositing the dye onto a surface that has been gently brushed or rubbed in a single direction. This patent reference also discloses that, by stretching a polymeric film, such as cellulose and derivatives thereof, proper orienting force may be obtained for dichroic dyes deposited thereon.
Light polarizing articles, such as polarizing ophthalmic lenses, have been manufactured by using various technologies and materials. Most of these products comprise a light polarizing layer in addition to a non-polarizing substrate. The polarizing layer is mostly formed from a dichroic material mentioned above. The light polarizing products hitherto produced and processes for the manufacture thereof have suffered from various drawbacks.
One problem of the prior art product is the distortion of the optical surface by the polarizing layer in the final product. Some of the light polarizing articles in the prior art are produced by laminating a pre-formed polarizing layer to a substrate. It is difficult, if not impossible, to allow the pre-formed polarizing layer to curve to a perfect fit with a contoured surface of the substrate, as is in the case of ophthalmic products. The less than perfect fit between the polarizing layer and the substrate can lead to undesired cylindrical power in an ophthalmic lens.
A second problem of the prior art process and products is delamination of the polarizing layer from the substrate during the manufacture process or during the life of the product. This is caused by, for example, (i) a less sufficient adhesion between the substrate and the polarizing layer; and/or (ii) stress between the layers having differing properties, especially differing thermal expansion coefficient.
Still another problem of the prior art polarizing product and processes for making them involves the leaching of substrate component into the polarizing layer. The leaching, or migration, can cause the deterioration of the mechanical and/or optical quality of the polarizing layer over time.
A fourth problem of the prior art article and process is the hazing of the article. Various causes contribute to this problem. The propagation and expansion of defects, optical and mechanical, originally on a micro-scale, is believed to be the leading culprit.
A fifth problem of the prior art article and process is the delamination between the polarizing dye layer and any additional coating applied over it, such as scratch-resistant coatings, hard coatings, water-repellant coatings, and the like.
European patent application publication No. 1674898 discloses a process for making polarizing articles. By depositing an inorganic adhesion-promoting layer between the lens substrate and the light polarizing dye layer, the invention disclosed therein solved the problem of poor adhesion between the substrate and the light polarizing dye layer.
Nonetheless, the issue of poor adhesion between the polarizing dye layer and the additional top layers remains to be solved. It has been found that adhesion between the polarizing dye layer and the additional functional layers, such as a hardcoat layer, can decrease during the life of the polarizing article over time on exposure to environmental factors, such as water, sweat, light, heat, and the like. Undesired premature delamination between these two layers may occur.
Consequently there is a genuine need for a polarizing article overcoming one or more drawback of the prior art and a process for making such articles.